1. Field of the Invention
The invention relates to apparatus and methods for influencing the fluid system of the inner ear for treating the symptoms of Meniere's disease or endolymphatic hydrops and, more particularly, to such apparatus and methods for treating symptoms of diseases and conditions of the ear, such as Meniere's disease or endolymphatic hydrops.
2. Description of the Related Art
Meniere's disease is a chronic disease from which millions of people suffer. The origin of Meniere's disease is believed to be an imbalance in the hydrodynamic system of the inner ear, described as endolymphatic hydrops. In addition to the severity of the symptoms of Meniere's disease, which include fluctuating hearing loss, fluctuating tinnitus, fluctuating sense of fullness in the ear and fluctuating vertigo, the unpredictable onset of the symptoms creates a major handicap for sufferers of Meniere's disease.
As illustrated in FIG. 1, the human ear 10 includes three primary spaces, the outer ear canal 12, also known as the external acoustic meatus, the middle ear 14, and the inner ear 16. The middle ear, also known as the tympanic cavity, is adjacent the outer ear canal and is separated from the outer ear canal by the tympanic membrane 18, also known as the ear drum. The inner ear includes the cochlea 20 formed of the scala vestibuli 22 and the scala tympani 24 which surround the cochlear duct 26 (cross-hatched to simplify visualization). The cochlear duct is filled with endolymphatic fluid supplied by the endolymphatic sac 28. The scala vestibuli 22 and scala tympani 24 are filled with perilymph fluid that moves in response to displacement of the footplate or base 29 of the stapes 30 in the oval window 32. The stapes is one of a series of small bones (ossicles) in the middle ear connecting the tympanic membrane 18 with the inner ear. The inner ear is separated from the middle ear by an anatomical partition formed of the stapes footplate 29 at the oval window 32 and the round window membrane 34. Since the stapes footplate is part of the stapes, the entire stapes may be considered as forming part of the partition. Movement of the stapes footplate in the oval window 32 causes the perilymph fluid to move within the scala vestibuli affecting the endolymphatic fluid within the cochlear duct to effect hearing. The round window membrane 34 separates the scala tympani 24 of the inner ear from the middle ear 14 and operates to dissipate waves formed in the perilymph fluid.
The symptoms of Meniere's disease are believed to be caused by endolymphatic hydrops, an excessive buildup of endolymphatic fluid in the cochlea. Meniere's disease is typically characterized by varying degrees of four classic symptoms: 1) fluctuating hearing loss, the extent of which increases over time; 2) fluctuating tinnitus, causing various sounds, described as whining, roaring or other sounds; 3) fluctuating sense of fullness, or a “plugged ear” sensation similar to a sensation one experiences upon descending from a mountain and being unable to clear or equalize the pressure in one's ear; and 4) fluctuating vertigo, or dizziness that can range from mild to severe. As used herein, the terms “symptoms of Meniere's disease” means some or all of the above symptoms in that the method and apparatus of the present invention can provide treatment for any of the above symptoms, individually or together, which are caused by endolymphatic hydrops.
An early method of treating a person with Meniere's disease was developed empirically and includes placing the patient in a pressure chamber to alleviate the symptoms. The theory of the treatment is to place pressure on the inner ear fluids to attempt to reduce the amount of fluid in the endolymph system, specifically the endolymph fluid within the scala media (not shown) of the cochlear duct 26.
Another method includes applying air pressure pulses to the middle ear by way of a hole through the tympanic membrane. The hole allows the pressure pulses to pass from the outer ear canal into the middle ear. It is believed that the round window membrane moves in response to the pressure changes and transfers the movement/pressure changes to the perilymph fluid, which resultantly transfers the motion/pressure to the endolymph fluid through membranes separating those two distinct fluids. The oval window may also act to transfer varying pressure to the perilymph fluid; and, accordingly, hereinafter references to displacement of the round window membrane also are meant to include displacement of the stapes footplate at the oval window. U.S. Pat. No. 4,757,807, WO Publications No. 83/02556, No. 93/08775, No. 97/23178, No. 00/01331, No. 00/01346 and No. 00/10484, European Patent No. 266474 B1, Acta Otolaryngol 102:186–193, 1986, Acta Otolaryngol 91:55–64, 1981, Acta Otolaryngol 102:403–409, 1986, Laryngoscope V.92, No. 11, 1982; 1285–92, Carlborg et al 1982 V. 91, No. 2, American Journal of Otology 18:726–733, Acta Otolaryngol 2000 543:99–101 and Acta Otolaryngol 2001 121:616–621 are representative of the above method which is also exemplified by the Meniett portable pressure pulse generator sold by Medtronic Xomed, Inc., Jacksonville, Fla.
In order to practice the above method, a hole formed in the tympanic membrane 18 is fitted with a ventilation tube 36, as shown in FIG. 1. After the ventilation tube 36 is inserted into the tympanic membrane, pressure pulses are generated and transmitted into the outer ear canal 12 by way of a tube having an ear plug sealing the tube against the walls of the outer ear canal so that the pressure pulses vary the pressure in the middle ear through the vent formed by the ventilation tube to influence the fluid system of the inner ear through the round window membrane. That is, the ventilation tube 36 allows air to pass from the outer ear canal 12 to the middle ear 14, thereby allowing the pressure pulses applied to the outer ear canal to cause the pressure in the middle ear to fluctuate. Although the actual mechanisms are still not fully understood, one theory of action that reduces endolymphatic hydrops is that the action of the pressure pulses on the fluid system combine with other physiologic reactions in the ear to force excess endolymph fluid into the endolymphatic sac 28.
The above method of treating Meniere's disease relies on applying a series of pressure pulses biased by a positive pressure Ps, as illustrated in FIG. 2. The pressure pulses are applied to the outer ear canal to transmit varying pressure changes through the ventilation tube 36 into the middle ear in order to displace the round window membrane 34. The series of pressure pulses developed as a result of empirical observations have been used to treat patients suffering from Meniere's disease.
The pressure pulses applied in the past have included sine waves, static and alternating components, a predetermined overpressure superimposed on pressure oscillations, square waves and low frequency sine waves superimposed on square wave pressure pulses. The Densert et al U.S. Pat. No. 6,159,171 shows pressure pulses generated by the Meniett portable pressure pulse generator in FIG. 3 thereof and provides a description thereof in columns 3 and 4.